Concentration of ores



alcoholic hydroxy groups.

Patented July, 8, 1941 Willem Coltof, Amsterdam,

' Netherlands, as-

signor to Shell Development Company, Sanv Francisco, Calif., a corporation of Delaware No Drawing.

Serial No. 208,490. tion September 11, 1

Original al plication May 17, 1938, Divided and this applica- 939, Serial No.

Great Britain May 29, 1937 6 Claims. (Cl. 209166) This invention relates to a process for the froth flotation of heavy metal-bearing ores, such as copper-bearing ores, which comprises subjecting.

such an ore to a froth flotation operation in the presence of a cyclic-organo-trithiocarbonate. By the term heavy metal, I mean any metal which has a specific gravity greater than four (Hackhs,-

Chemical Dictionary, 2nd edition, page 443) By cyclic-organo-trithiocarbonates, I mean trithiocarbonates in which the two thiol sulfur atoms are members of aheterocyclic ring.

Trithiocarbonates may be synthesized by several methods. The known methods, however, require costly reagents, are-usually inv :d, and are not generally suited for com Thus, for example, ethylene trithi been prepared by reacting sodiu: ethylene dimercaptide with carbon disulfide, by reacting ethylene bromide with sodiumtrithiocarbonate in absolute alcohol, and by more complicated syntheses. In order to prepare trithiocarbonates from carbon disulfide it has always been considered necessary to react the same with a compound containing the structural grouping .conate has .al use.

better stability of the cyclic trithiocarbonates 1 formed, I prefer to use such compounds as constable derivatives such as, for instance, ethylene mercaptan, dithio catechol, etc. Reagents having this dithiol structure are diiiicult to prepare, not readily available, and consequently costly.

I have found, contrary to expectation and the teaching of the art, that, in general, good yields of cyclic-organo-trithiocarbonates may be prepared by reacting carbon disulflde with organic diol compounds, i. e., compounds containing two found that it is notnecessary first to prepare the 'diol compound since any derivative thereof which in.the presence of water and an alkali is capable of yielding the diol compound is equally applicable. I

As examples of derivatives of diol compounds may be mentioned those compounds in which one or both of the reactive alcoholic hydroxy groups placed by any group or groups which, under the influence of water and alkali, tend to form hydro y groups.

In view of the better yields obtainable and the tain the reacting hydroxy or hydrolyzable groups attachedto carbonv atoms which arenot more than once removed. Thesecompounds react with carbon disulfide to forni the very stable cyclicorgano-trithiocarbonates containing the relatively unstrained five and six-membered heterocyclic ring structure. My process is, however, applicable to the preparation of cyclic-organetrithiocarbonates from carbon disulfide and such compounds as contain the hydroxy or hydrolyzable groups either farther removed or on the same carbon atom. It is known, of course, that compounds containing two hydroxy groups attached to the same carbon atom are too unstable to be isolated. However, the cyclic-organo trithiocarbonate derivatives of these compounds containing a relatively stable four-membered ring may be prepared according to the present invention by reacting carbon disulfide with the of these unstable alcohols.

Thus, for example, methylene trithiocarbonate and homologues thereof may be prepared by utilizing methylenehalide and its homologues.

Of the applicable compounds which I may react with carbon disulfide to form 'cyclic-organotrithiocarbonate, those of aliphatic character, especially the'lower members, are the least expensive and most available raw materials and appear to give the best yields and, therefore, may be most advantageously employed in. the present I have, furthermore,

- has or have been esterified with an organic or etc., the glycol estersof process. Of these compounds, those which contain the reactive hydroxy or hydrolyzable groups attached to non-tertiary carbon atoms appear to give the best yields and the most stable products. A tertiary carbon atom is one which is attached to three other carbon atoms. Thus, for example, I may advantageously employ the glycols, such as ethylene glycol, trimethylene glycol, 2-methyl trimethylen'e glycol, propylene 'glycol, buty lene glycol, butane-2 glycol, etc., the

alkene 0Xides,sllch as e hylene oxide, propylene oxide, trimethylene oxide, butylene oxide, butadiene' ethylene bromide, trimethylene bromide, propylene chloride, trichlorethane, etc., the alkene halohydrins, such as ethylene chlorhydrin, trimethylene chlorhydrin, amylene' chlorhydrins, organic "acids, such as trimethylene glycol monoacetate, ethylene glycol diacetate, beta chlor ethylacetate, etc., the glycol esters of inorganic acids,

dioxide, etc., the 'alkene halides, such as such as ethylene glycol disulfate, beta chlor ethyl sulfate, etc., the glycolates, such as sodium ethylene glycolate, etc.

Thus, it is seen that, while the prior processes react carbon disulfide with a compound containing two thiol groups, I utilize compounds containing two alcoholic hydroxy. groups or any of the inexpensive and available compounds, which, in the presence of water and alkali, are capable of yielding such groups. Assuming the usual type reaction, the compounds used in the present method would be expected to react with carbon disulflde to produce derivatives of thion thiol carbonic acid. Thus, for example, by reacting ethylene glycol with carbon disulfide, one would expect ethylene thiol-thion-carbonic acid to be formed according to the equation:

' H2C-S HzC-H KQH +0 s1 o=s +H.0 HzC-OH HzC-O While I do not desire to be limited by the soundness of any theories advanced as to the mechanisms involved, I believe that the reaction proceeds in the expected manner and that, under the reaction conditions, the thiol-thion derivatives as soon as formed, react quantitatively with the reactants present to give the desired trithio- I have found that in order for the reaction to proceed, the presence of an alkali is necessary and that in order to obtain optimum yields, it is desirable that the quantityused be closely regulated. Thus,. the following results were obtained when reacting ethylene chloride with carbon disulfide in the presence of varying amounts of alkali.

Percent of theoretical M01 equiv. alkali used yield CO moo cvez'heazco I have found the optimum yields to be obtained when the quantity of alkali used is near the stoichiometric amount. The stoichiometric amount of alkali, as can be seen from the above probable reaction mechanism, is two mol equivalents per mol of organic reactant plus one mol equivalent for each hydrolyzable group in the organic reactant. Thus, for ethylene glycol the stoichiometric quantity is two mol equivalents, for ethylene chlorhydrin three mol equivalents, for ethylene chloride and trichlorethane four mol equivalents, etc.

The preparation of the cyclic-organo-trithe alkali metal hydroxides, alkaline earth oxides, metal alcoholates, alkali metal carbonates, alkali metal rhodanides, etc., may be employed. I have noticed, however, that thestronger bases, such as sodium and potassium hydroxides, appear to hasten the reaction and their use may, therefore, be preferred.

The cyclic-organo-trithiocarbonates are preferably prepared in the presence of at least enough water to allow the hydrolysis when compounds containing hydrolyzable groups are employed. A substantial excess of water, however, although unnecessary, is in no way detrimental.

The mol ratio 'of carbon disulflde to organic reactant employed appears to affect the yield to some extent. I have found that, in general, somewhat better yields are obtained when this ratio is two or greater. giving somewhat lower yields, may, however, be used.

The ethylene trithiocarbonate forms goldcolored needles melting at about 34 C. and has thiocarbonates is not restricted to the use of any particular alkali. Thus, for example, any of a remarkably high refractive index, viz. 1.79. In determining its density in water by the displacement method, I noticed that this substance, both in a crystalline and in a molten state, obstinately retained air bubbles at its surface. When poured into a glass vessel as a liquid, its meniscus was convex. In view of the remarkable properties of this compound and the excellent yield obtained, I have studied the preparation and use of cyclic-organo-trithiocarbonates in general.

In view of the tenacity with which ethylene trithiocarbonate retained air bubbles when wetted with water, the cyclic-organo-trithiocarbonates were tested as to their efficiency as flotation agents. Preliminary tests showed cyclic-organo-trithiocarbonates, especially the lower members, to compare favorably with the best flotation agents known to the art for the flotation of heavy metal-bearing ores, such as the copper ores, and particularly for the flotation of the heavy metal-bearing sulfidi'c and/or oxidic ores.

The excellent activity of the cyclic-organotrithiocarbonates as collectors in ore flotation is quite unexpected when it is considered that it has heretofore been assumed that the highest activity resulted from substances possessing a strongly polar part side by side with a non-polar part in the molecule. Thus, for example, the presence of a free salt-forming group was considered to be highly conducive to, if not essential for, a satisfactory activity. Now the present cyclic-organo-trithiocarbonates, although not possessing such a. group, even surpass, for some cases, the very active alkali trithiocarbonates and the alkali xanthates in activity. I

Example I A mixture consisting of 2 gm. mols of KOH, 1

gm. mol of CS2, gm. mol of ethylene chloride.

Lower ratios, although 2,248,912 and 250 cm. water was refluxed at 50 to 55 C.,

while stirring for about 3 hours. At the end of a this time, the refluxing of the CS2 being terminated, the temperature was raised to 95 C. and maintained for two hours. The resulting reaction mixture separated into two layers. The lower layer was taken up in benzene, washed with water, the greater part of the benzene removed by distillation, and the product poured into ligroin, whereupon the ethylene trithiocarbonate was precipitated in the form of yellow crystals. The yield amounted to 65 grams, which corresponds to a theoretical yield of 95%.

Example II Ethylene chlorhydrin, sodium sec. decyl alcoholate, and carbon disulflde in equimolar quantities were reacted in the presence of water as in the above example. The yield of ethylene trithiocarbonate was 60% of the theoretical. It should be noted that the ratios of the reactants used in this experiment are not the optimum.

Example III A mixture consisting of 2 gm. mols KOH, '1 gm: mol CS2, gm. mol 1.2-dichloro propane and 250 cm. water was reacted as in Example I. The yield of propylene trithiocarbonate was 69% of the theoretical.

Example IV 62 grams of CaO were slaked in 250 cm. water, then 76 grams of CS2 and 50 grams of ethylene chloride were added while stirring and refluxing. After 2 hours the refluxing of the CS2 was terminated, and the mixture was then heated during four hours at 75 C. From the resulting reaction mixture, which consisted of two layers, ethylene trithiocarbonate was recovered by extraction with benzene in a yield of about 25 grams.

Example V Example VI 66 grams of KOH, 76 grams of CS2, 22 grams of ethylene oxide and 250 cm. water were reacted in the same manner as described in Example V. The reaction mixture, when extracted with benzene, yielded about 20 grams of ethylene trithiocarbonate.

' Example VII To a solution of 7 grams of sodium in 100 cm. methanol 162.5 grams of glycol were added. From the resulting mixture the methanol was removed by vacuum distillation at 50 C. and then 40 grams of CS2 were added in drops to the reaction product in a nitrogen atmosphere while stirring. After hours refluxing at 55 C. the mixture was heated for a further 9 hours at 95 C. .By extraction of the reaction products with benzene 11 grams of ethylene trithiocarbonate were obtained.

Ewample VIII To a mixture of 45 grams of potassium rhodanide, 45 grams of water and 30 grams of ethylene oxide, 35 grams of CS2 were slowly added at -5 C. and subsequently the temperature was raised in 2 hours to 20 C. In the next 2 hours the temperature rose to 45 C. and then it rapidly increased to 105? C. Stirring was continued for another 2 hours, during which the reaction mixture cooled down to room temperature. By working up the reaction mixture, about 38 grams of ethylene trithiocarbonate were recovered. It is probable that ethylene sulfide is formed intermediately, which subsequently reacts with CS2, under formation of ethylene trithiocarbonate.

Example IX A copper ore containing 3.97% of sulfidic copper and 0.87% oxidic copper, was subjected to a flotation operation, whilst using per ton of ore 70 g. of ethylene trithiocarbonate as collector and a slight amount of pine oil as frothing agent. The yield based on the weight of the ore treated was 5.84% concentrate containing 46.88% sulfidic copper and 2.52% oxidic copper and 3.67% of a concentrate containing 32.00% sulfidic copper and 8.00% oxidic copper. The extraction thus amounted to about 90% total copper, viz. 98.6% sulfidic copper and 50.7% oxidic copper.

When treating the same ore whilstusing xanthates as flotation agents, the copper content of the concentrates was considerably lower.

This application is a division of my copending application, Serial No. 208,490, filed May 17, 1938.

I claim as my invention: r

1. In a process for concentrating sulfide ores bearing heavy metals by flotation, the step which comprises subjecting the ore in the form of a pulp to a froth flotation operation in the presence of ethylene trithiocarbonate containing the trithiocarbonate group in a heterocylic ring.

2. In a process for concentrating ores bearing copper by flotation, the step which comprises subjecting the ore to a froth flotation operation in the presence of an alkene trithiocarbonate containing the trithiocarbonate group in a heterocylic ring.

3. In a process for concentrating heavy metalbearing ores by flotation, the step which comprises subjecting the ore in the form of a pulp to a froth flotation operation in the presence of a cyclic-organo-trithiocarbonate containing the trithiocarbonate group in a heterocyclic ring.

4. In' a process for concentrating sulfide ores bearing heavy metals by flotation, the step which comprises subjecting the ore to a froth flotation operation. in the presence of a cyclic-organotrithiocarbonate consisting of a divalent organic group linked to a trithiocarbonate group.

5. In a process for concentrating sulfide ores bearing heavy metals by flotation, the step which comprises subjecting the ore in the form of a pulp to a froth flotation operation in the presence of an alkene trithiocarbonate containing the trithiocarbonate group in a heterocyclic ring.

6. In a process for concentrating ores bearing heavy copper sulfide by flotation, the step which comprises subjecting the ore in the form of a pulp to a froth flotation operation in the presence of ethylene trithiocarbonate containing the trithiocarbonate group in a heterocyclic ring.

. WILLEM COLTO F.

Certificate of Correction Patent No. 2,248,912. July 8, 1941.

WILLEM COLTOF It is hereby certified that errors appear in the printed specification of the above numbered patent requiring correction as follows: Page 2, first column, lines 3639, in the formula, for

Hie-s Bic-s C=S read I O=S HaC-S Hz(i1S page 3, second column, line 41 and lines 46-47, claims 1 and 2 respectively, for heterocylic read heterocyclz'c; and that the said Letters Patent should be read with these corrections therein that the same may conform to the record of the case in the Patent O'ifice.

Signed and sealed this 30th day of Sept ember, A. D. 1941.

HENRY VAN ARSDALE,

Acting Oomwnissz'oner of Patents. 

